Ferromagnetic Transition in a Caged Compound NdOs2Zn20

AbstractMagnetic properties in a caged compound NdOs2Zn20 have been studied by the measurements of magnetization M, magnetic susceptibility M/B, and specific heat C. The measurements indicate that NdOs2Zn20 shows a structural transition at Ts = 62K and a ferromagnetic transition at TC = 0.6K. The structural transition is also observed in the La counter-part LaOs2Zn20 at Ts = 151K. The results of M (T)/B, M (B), and C(T) of NdOs2Zn20 are reproduced by a crystalline electrical field scheme with a Kramers doublet ground state

Elastic Response in the Dilute non-Kramers System Y1−x_{1-x}Prx_xIr2_2Zn20_{20}

Ultrasonic investigations of the single-site quadrupolar Kondo effect in diluted Pr system Y$_{0.966}$Pr$_{0.034}$Ir$_2$Zn$_{20}$ are reported. The elastic constant $(C_{11}-C_{12})/2$ is measured down to ~40 mK using ultrasound for the dilute system Y$_{0.966}$Pr$_{0.034}$Ir$_2$Zn$_{20}$ and the pure compound YIr$_2$Zn$_{20}$. We found that the elastic constant $(C_{11}-C_{12})/2$ of the Pr-dilute system exhibits a logarithmic temperature dependence below $T_0$ ~0.3 K, where non-Fermi-liquid (NFL) behavior in the specific heat and electrical resistivity is observed. This logarithmic temperature variation manifested in the $\Gamma_3$-symmetry quadrupolar susceptibility is consistent with the theoretical prediction of the quadrupolar Kondo effect by D. L. Cox. On the other hand, the pure compound YIr$_2$Zn$_{20}$ without $4f$-electron contributions shows nearly no change in its elastic constants evidencing negligible phonon contributions. In addition, clear acoustic de Haas-van Alphen (dHvA) oscillations in the elastic constant were detected for both compounds on applying magnetic field. This is mainly interpreted as contribution from the Fermi surface of YIr$_2$Zn$_{20}$.Comment: 9 pages, 4 figures, Proceedings of J-Physics 2019 International Conferenc

Off-center rattling and thermoelectric properties of type-II clathrate (K, Ba)(24)(Ga, Sn, square)(136) single crystals

We report the synthesis and temperature-dependent structural, transport, and thermal properties of type-II clathrate K8+xBa16-xGa40-ySn96-z square(y+z) (1.2 <= x <= 2.8, 2.0 <= y <= 3.3, 0.8 <= z <= 6.6, square = framework vacancy). Single-crystal x-ray diffraction analysis reveals that the guest K+ and Ba2+ ions are preferentially incorporated into the hexakaidecahedral cages and dodecahedral cages, respectively. The guest site in the former splits into four sites 0.67 angstrom away from the center to the 32e site of the cage. The splitting is consistent with the presence of four minima in the electrostatic potential in the hexakaidecahedron. The thermopower is negative and relatively large, -50 similar to -120 mu V/K at 300 K, indicating that the dominant charge carriers are electrons. The thermal conductivity displays a glasslike behavior with a plateau at around 20 K. The analysis of the specific heat indicates that the motion of the K+ ion in the hexakaidecahedron can be described by the soft-potential model, including the tunneling term. The characteristic energy of 21 K for the soft mode is as low as that of the off-center rattling of the Ba2+ ion in type-I clathrate Ba8Ga16Sn30. The present result on the type-II clathrate verifies the idea that the low-energy off-center rattling in oversized cages of intermetallic clathrates couples to the acoustic phonons to lead to the glasslike thermal conductivity

Inelastic neutron scattering study of crystalline electric field excitations in the caged compounds NdT2Zn20 (T = Co, Rh, and Ir)

We have measured crystalline electric field (CEF) excitations of Nd3+ ions in the two-channel Kondo lattice candidates NdT2Zn20 (T = Co, Rh, and Ir) by means of inelastic neutron scattering (INS). In the INS measurements at 5 K, dispersionless excitations were observed at 3.8 and 7.2 meV for T = Co, 3.1 and 5.8 meV for T = Rh, and 3.0 and 5.3 meV for T = Ir. Analyses of the temperature dependence of the INS spectra confirm that the CEF ground states are the Gamma 6 doublet, that is a requisite for manifestation of the magnetic two-channel Kondo effect. For T = Co, a shoulder was observed at 7.7 meV close to the CEF excitation peak centered at 7.2 meV. The shoulder is attributed to a bound state of the CEF and low-lying optical phonon excitations.Comment: 6 pages, 3 figure

Neutron scattering study on spin correlations and fluctuations in the transition-metal-based magnetic quasicrystal Zn-Fe-Sc

Spin correlations and fluctuations in the 3d-transition-metal-based icosahedral quasicrystal Zn-Fe-Sc have been investigated by neutron scattering using polycrystalline samples. Magnetic diffuse scattering has been observed in the elastic experiment at low temperatures, indicating development of static short-range-spin correlations. In addition, the inelastic scattering experiment detects a $Q$-independent quasielastic signal ascribed to single-site relaxational spin fluctuations. Above the macroscopic freezing temperature $T_{\rm f} \simeq 7$ K, the spin relaxation rate shows Arrhenius-type behavior, indicating thermally activated relaxation process. In contrast, the relaxation rate remains finite even at the lowest temperature, suggesting a certain quantum origin for the spin fluctuations below $T_{\rm f}$.Comment: To be published in Phys. Rev.